The Impact of Different Grid Size Values and Dose Calculation Algorithms on Plan Accuracy in Vmat-Based Radiotherapy for Breast Cancer

This study evaluated the impact of dose calculation algorithms (Monte Carlo and Pencil Beam) and grid size values (1.5 mm, 3 mm, and 5 mm) on the accuracy of VMAT-based radiotherapy plans for breast cancer. Six different treatment plans were generated for each patient using combinations of algorithm and grid size values. The plan created with the Monte Carlo algorithm and a 1.5 mm grid size was designated as the reference plan, and all other plans were compared dosimetrically to this baseline. Results showed that both the choice of algorithm and grid size significantly influenced dose distribution in target volumes (PTVs) and organs at risk (OARs). For example, the D%98 value of the PTVmeme in the reference plan was 47.2 ± 1.0 Gy, which decreased to 44.4 ± 1.4 Gy in the Pencil Beam plan with a 5 mm grid size. For OARs, algorithm selection had a more pronounced impact. The V20 of the ipsilateral lung was 24.2 ± 0.9% in the reference plan but dropped to 20.3 ± 1.2% in the Pencil Beam plan with a 1.5 mm grid size (p